Remote recorders have been available to record various environmental conditions. In one application, temperature recorders are available which can record environmental temperature over a specific time period and provide a readout of the measured temperature versus time.
Typically, such recorders have been of the chart recorder type. These recorders inscribe a graph of measured temperature versus time on a rolling strip chart. When the measurements are complete, the user can remove the inscribed script chart from the recorder unit and determine the temperature history of the recorder. This type of chart recorder has been used for measuring the temperature of cargo containers for fruits, vegetables and other temperature-sensitive produce. The recorder is usually placed with the produce to be shipped and retrieved at the end of the trip by the receiver. The recorder also typically includes some type of security mechanism to prevent the shipper from tampering with the recorder during transit.
Recorders of the type discussed above suffer from a number of disadvantages which have become well known to those in the industry. The recorder mechanism itself can be unreliable in that a number of moving parts are required to operate the moving pen and rolling strip chart. While great strides have been made in perfecting the reliability of these devices, the inherent disadvantage of moving parts has not been overcome. Furthermore, the security measures provided for such devices are far from tamper proof. A shipper need only break the external security seal on such device to replace the strip chart with a falsified chart. Upon resealing the device, the receiver is unable to detect any violation of the recorder unit.
It has been suggested that temperature data of the type described above can be remotely recorded by an electronic device. The implementation of such a recorder has been heretofore impractical because of the ease with which one well versed in electronics can defeat the data integrity of such an electronic system. Therefore, a need exists for an electronic remote environmental monitoring system which has redundant safeguards to protect the integrity of the stored data.